Tc – This is a time interval in milliseconds when a Committed Burst (Bc) can get sent. Usually Tc = Bc / CIR
Bc – Committed Burst this is the amount of data in bits which can bet sent every Tc. Usually Bc = CIR / Tc
Be – Excess Burst is the number of bits the Bc can be exceed by if no data has been sent if no data has been sent in previous Tcs. EDIT: As commented by Jeriel Atienza the formula is Be = (Ar – CIR) * Tc/1000
CIR – Committed Information Rate this is the bandwidth of a link or VC in bps which the Service Provider guarantees to provide. Quite often the CIR is lower than the full capabilities of a link which is the main reason why traffic should be shaped & policed. CIR = Bc * Tc
Shaped Rate – This is the rate of the traffic which is being shaped in bps, it normally matches the CIR. Usually CIR = Shaped Rate!